Two new cytokines which have been designated as Oncoimmunin-L (MW 45kD) and Oncoimmunin-M (MW 36 kD) were identified and purified to homogeneity by SDS-PAGE analysis from a tumor cell supernatant. To achieve this end, combinations of ion exchange, gel filtration, hydrophobic interaction, and reverse phase chromatography were implemented. Oncoimmunin-L is a human T-lymphocyte mitogen and Oncoimmunin-M inhibits the growth of at least three human myeloid leukemic cell lines. Concomitantly with the inhibition of proliferation, the latter factor induces the cell surface expression of the integrin CD11 and migration of cells toward a chemotactic gradient. Results from this project which was aimed at exploring the possible presence of soluble immunoregulatory factors of tumor origin support the idea that the tumor immunoenvironment as recognized by immunocytes is defined by soluble mediators in addition to the well-studied cell-cell contact interactions.